(a) Field of the Invention
The present invention relates to a polyurethane resin, a foam prepared from the resin, a preparation process of the foam, and a polyurethane foam composite fitted with a face material. In the manufacture of rigid polyurethane foams, the novel polyoxyalkylene polyol prepared according to the present invention is excellent in mutual dispersibility when the polyol is mixed with a hydrochlorofluorocarbon which can minimize environmental destruction, and has good workability. In addition, a polyurethane resin prepared by reacting the polyoxyalkylene polyol with an organic polyisocyanate in the presence of a catalyst, if necessary, has good resistance to dissolving into a hydrochlorofluorocarbon, and hence can provide extremely favorable effects. For example, the polyurethane foam prepared from the novel polyoxyalkylene polyol has excellent physical properties such as heat insulation property, strength, low temperature dimensional stability and flame resistance. Consequently, the polyurethane foam is very useful for various applications such as refrigerators, freezers, heat insulation panels and other adiabatic structural materials.
(b) Description of the Prior Art
Rigid polyurethane foam has an excellent heat insulation property and low temperature dimensional stability and thus various composites prepared therefrom are widely used for refrigerators, freezing ware houses, building wall faces, ceilings, heat insulation and structural materials for ships and vehicles, and the heat insulating and protective covers of instruments.
Further, composites containing rigid polyurethane foam formed on a sheet of face material or in a cavity surrounded by a plurality of face material have already been broadly manufactured by a batch process or a continuous process.
In the present manufacturing processes for polyurethane foams, furon, particularly chlorofluorocarbons (hereinafter abbreviated as CFC) as CFC-11 and CFC-12 are generally used as foaming agents. These compounds have recently been recognized as materials for causing environmental destruction such as disruption of ozone layer or for enhancement of green house effect. Accordingly, restrictions have recently been imposed upon the manufacture and use of these compounds.
At the same time, hydrochlorofluorocarbons (hereinafter abbreviated as HCFC) such as 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b) which cause much less environmental destruction, have been the focus of attention as substitutes for CFC-11 and CFC-12. However, HCFC-123 and -141b have higher dissolving effect on polyurethane resin compared to CFC-11 and -12, and hence, have the disadvantage of severely deteriorating the properties of resulting polyurethane foams (e.g., reduction of closed cell content and foam strengths). Particularly, this is the case in the manufacture of rigid polyurethane foams. HCFC dissolves the cell wall of closed cells in the course of foaming and drastically lowers heat insulation effect which is a characteristic property of rigid polyurethane foams.
Consequently, development of novel polyurethane resins and foams which can be used in combination with HCFC has been desired. In the preparation of polyoxyalkylene polyols for use in the manufacture of conventional polyurethane resins, a polyoxyalkylene polyol obtained by the addition of alkylene oxide to novolak resin has been proposed to be used in combination with polyether polyol or polyester polyol, as disclosed in Japanese Patent Publication Nos. SHO 46-3797(1971) and SHO 47-19911(1972) and Japanese Patent Laid-Open Publication Nos. SHO 63-264616(1988) and HEI 1-135824(1989).
In any of these disclosures, novolak base polyols are singly used in order to improve flame resistance of polyurethane foams. No description has been found on the use of phenol resin in a specific combination with alkanolamine or polyoxyalkylene polyol using an aliphatic polyhydroxy compound as an starting material. Also, no disclosure has been found on the improvement of dissolving resistance of polyurethane resin to HCFC-123 and HCFC-141b and improvement of physical properties of polyurethane foams using these HCFC compounds as a foaming agent.
As mentioned above, HCFC which is much less dangerous for environmental destruction, has a strong dissolving effect on polyurethane resin and is liable to result in deterioration of foam properties and reduction of closed cell content. Consequently, satisfactory foam properties have not been obtained.
In the manufacture of rigid polyurethane foams, application of HCFC-123 or HCFC-141b as a foaming agent in place of CFC-11 leads to various unfavorable problems.
(1) Reaction rate becomes slow. As a result, when a surface to be sprayed by polyurethane liquid raw materials is not horizontally situated, the sprayed raw materials causes sagging or running on the surface prior to foaming and curing.
(2) Polyurethane foams which are obtained cause remarkable deterioration of physical properties such as low temperature dimensional stability and compressive strength.
(3) A marked increase in heat conductivity is observed on the polyurethane foam obtained.
Polyurethane foams and their composites having the above problems naturally causes reduction of quality.